Trump said Graham “lost it” during an appearance on Fox News this morning in which the senator called Trump a “kook,” “crazy” and “unfit for office.”

“At the end of the day, he would be the most flawed nominee in the history of the Republican Party,” said Graham, who is backing Jeb Bush.

In response, Trump declared Graham the “dumbest human being.”

“He went crazy,” Trump told the crowd at his first event of the day. “The guy is a nut job.”

The real estate mogul, who is holding onto a wide lead in the polls ahead of the Palmetto State’s Saturday GOP primary, went on to say he doesn’t want an endorsement from the South Carolina senator, let alone “anything to do with him.”

“I could push him over with a little thimble,” Trump snapped, adding later in his remarks: “I don’t think he could run for dogcatcher in this state and win again. I really don’t.”

Graham has been campaigning with Bush and said in an interview on ABC News' “Good Morning America” earlier this week that he would have to “re-evaluate” whether to support Trump were he to become the GOP nominee.